/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 1997-2008 Sun Microsystems, Inc.  Portions Copyrighted 2008 Richard Schilling.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License. You can obtain
 * a copy of the License at https://glassfish.dev.java.net/public/CDDL+GPL.html
 * or glassfish/bootstrap/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at glassfish/bootstrap/legal/LICENSE.txt.
 * Sun designates this particular file as subject to the "Classpath" exception
 * as provided by Sun in the GPL Version 2 section of the License file that
 * accompanied this code.  If applicable, add the following below the License
 * Header, with the fields enclosed by brackets [] replaced by your own
 * identifying information: "Portions Copyrighted [year]
 * [name of copyright owner]"
 *
 * Contributor(s): Richard Schilling (coderroadie@gmail.com)
 *
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.mail.util;

import java.io.*;

/**
 * This class implements a BASE64 Decoder. It is implemented as
 * a FilterInputStream, so one can just wrap this class around
 * any input stream and read bytes from this filter. The decoding
 * is done as the bytes are read out.
 * 
 * @author John Mani
 * @author Bill Shannon
 */

public class BASE64DecoderStream extends FilterInputStream {

    // buffer of decoded bytes for single byte reads
    private byte[] buffer = new byte[3];
    private int bufsize = 0;	// size of the cache
    private int index = 0;	// index into the cache

    // buffer for almost 8K of typical 76 chars + CRLF lines,
    // used by getByte method. this buffer contains encoded bytes.
    private byte[] input_buffer = new byte[78 * 105];
    private int input_pos = 0;
    private int input_len = 0;;

    private boolean ignoreErrors = false;

    /**
     * Create a BASE64 decoder that decodes the specified input stream.
     * The System property <code>mail.mime.base64.ignoreerrors</code> controls
     * whether errors in the encoded data cause an exception
     * or are ignored. The default is false (errors cause exception).
     * 
     * @param in the input stream
     */
    public BASE64DecoderStream(InputStream in) {
        super(in);
        // default to false
        ignoreErrors = PropUtil.getBooleanSystemProperty("mail.mime.base64.ignoreerrors", false);
    }

    /**
     * Create a BASE64 decoder that decodes the specified input stream.
     * 
     * @param in the input stream
     * @param ignoreErrors ignore errors in encoded data?
     */
    public BASE64DecoderStream(InputStream in, boolean ignoreErrors) {
        super(in);
        this.ignoreErrors = ignoreErrors;
    }

    /**
     * Read the next decoded byte from this input stream. The byte
     * is returned as an <code>int</code> in the range <code>0</code> to
     * <code>255</code>. If no byte is available because the end of
     * the stream has been reached, the value <code>-1</code> is returned.
     * This method blocks until input data is available, the end of the
     * stream is detected, or an exception is thrown.
     * 
     * @return next byte of data, or <code>-1</code> if the end of the
     *         stream is reached.
     * @exception IOException if an I/O error occurs.
     * @see java.io.FilterInputStream#in
     */
    public int read() throws IOException {
        if (index >= bufsize) {
            bufsize = decode(buffer, 0, buffer.length);
            if (bufsize <= 0) // buffer is empty
                return -1;
            index = 0; // reset index into buffer
        }
        return buffer[index++] & 0xff; // Zero off the MSB
    }

    /**
     * Reads up to <code>len</code> decoded bytes of data from this input stream
     * into an array of bytes. This method blocks until some input is
     * available.
     * <p>
     * 
     * @param buf the buffer into which the data is read.
     * @param off the start offset of the data.
     * @param len the maximum number of bytes read.
     * @return the total number of bytes read into the buffer, or
     *         <code>-1</code> if there is no more data because the end of
     *         the stream has been reached.
     * @exception IOException if an I/O error occurs.
     */
    public int read(byte[] buf, int off, int len) throws IOException {
        // empty out single byte read buffer
        int off0 = off;
        while (index < bufsize && len > 0) {
            buf[off++] = buffer[index++];
            len--;
        }
        if (index >= bufsize)
            bufsize = index = 0;

        int bsize = (len / 3) * 3;	// round down to multiple of 3 bytes
        if (bsize > 0) {
            int size = decode(buf, off, bsize);
            off += size;
            len -= size;

            if (size != bsize) {	// hit EOF?
                if (off == off0)	// haven't returned any data
                    return -1;
                else
                    // returned some data before hitting EOF
                    return off - off0;
            }
        }

        // finish up with a partial read if necessary
        for (; len > 0; len--) {
            int c = read();
            if (c == -1)	// EOF
                break;
            buf[off++] = (byte) c;
        }

        if (off == off0)	// haven't returned any data
            return -1;
        else
            // returned some data before hitting EOF
            return off - off0;
    }

    /**
     * Skips over and discards n bytes of data from this stream.
     */
    public long skip(long n) throws IOException {
        long skipped = 0;
        while (n-- > 0 && read() >= 0)
            skipped++;
        return skipped;
    }

    /**
     * Tests if this input stream supports marks. Currently this class
     * does not support marks
     */
    public boolean markSupported() {
        return false; // Maybe later ..
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking. However, this figure is only
     * a close approximation in case the original encoded stream
     * contains embedded CRLFs; since the CRLFs are discarded, not decoded
     */
    public int available() throws IOException {
        // This is only an estimate, since in.available()
        // might include CRLFs too ..
        return ((in.available() * 3) / 4 + (bufsize - index));
    }

    /**
     * This character array provides the character to value map
     * based on RFC1521.
     */
    private final static char pem_array[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
    'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
    'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
    'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
    'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
    'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
    'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
    '4', '5', '6', '7', '8', '9', '+', '/'  // 7
    };

    private final static byte pem_convert_array[] = new byte[256];

    static {
        for (int i = 0; i < 255; i++)
            pem_convert_array[i] = -1;
        for (int i = 0; i < pem_array.length; i++)
            pem_convert_array[pem_array[i]] = (byte) i;
    }

    /**
     * The decoder algorithm. Most of the complexity here is dealing
     * with error cases. Returns the number of bytes decoded, which
     * may be zero. Decoding is done by filling an int with 4 6-bit
     * values by shifting them in from the bottom and then extracting
     * 3 8-bit bytes from the int by shifting them out from the bottom.
     * 
     * @param outbuf the buffer into which to put the decoded bytes
     * @param pos position in the buffer to start filling
     * @param len the number of bytes to fill
     * @return the number of bytes filled, always a multiple
     *         of three, and may be zero
     * @exception IOException if the data is incorrectly formatted
     */
    private int decode(byte[] outbuf, int pos, int len) throws IOException {
        int pos0 = pos;
        while (len >= 3) {
            /*
             * We need 4 valid base64 characters before we start decoding.
             * We skip anything that's not a valid base64 character (usually
             * just CRLF).
             */
            int got = 0;
            int val = 0;
            while (got < 4) {
                int i = getByte();
                if (i == -1 || i == -2) {
                    boolean atEOF;
                    if (i == -1) {
                        if (got == 0)
                            return pos - pos0;
                        if (!ignoreErrors)
                            throw new DecodingException("BASE64Decoder: Error in encoded stream: "
                                    + "needed 4 valid base64 characters " + "but only got " + got
                                    + " before EOF" + recentChars());
                        atEOF = true;	// don't read any more
                    } else {	// i == -2
                        // found a padding character, we're at EOF
                        // XXX - should do something to make EOF "sticky"
                        if (got < 2 && !ignoreErrors)
                            throw new DecodingException("BASE64Decoder: Error in encoded stream: "
                                    + "needed at least 2 valid base64 characters,"
                                    + " but only got " + got + " before padding character (=)"
                                    + recentChars());

                        // didn't get any characters before padding character?
                        if (got == 0)
                            return pos - pos0;
                        atEOF = false;	// need to keep reading
                    }

                    // pad partial result with zeroes

                    // how many bytes will we produce on output?
                    // (got always < 4, so size always < 3)
                    int size = got - 1;
                    if (size == 0)
                        size = 1;

                    // handle the one padding character we've seen
                    got++;
                    val <<= 6;

                    while (got < 4) {
                        if (!atEOF) {
                            // consume the rest of the padding characters,
                            // filling with zeroes
                            i = getByte();
                            if (i == -1) {
                                if (!ignoreErrors)
                                    throw new DecodingException("BASE64Decoder: Error in encoded "
                                            + "stream: hit EOF while looking for "
                                            + "padding characters (=)" + recentChars());
                            } else if (i != -2) {
                                if (!ignoreErrors)
                                    throw new DecodingException("BASE64Decoder: Error in encoded "
                                            + "stream: found valid base64 "
                                            + "character after a padding character " + "(=)"
                                            + recentChars());
                            }
                        }
                        val <<= 6;
                        got++;
                    }

                    // now pull out however many valid bytes we got
                    val >>= 8;		// always skip first one
                    if (size == 2)
                        outbuf[pos + 1] = (byte) (val & 0xff);
                    val >>= 8;
                    outbuf[pos] = (byte) (val & 0xff);
                    // len -= size; // not needed, return below
                    pos += size;
                    return pos - pos0;
                } else {
                    // got a valid byte
                    val <<= 6;
                    got++;
                    val |= i;
                }
            }

            // read 4 valid characters, now extract 3 bytes
            outbuf[pos + 2] = (byte) (val & 0xff);
            val >>= 8;
            outbuf[pos + 1] = (byte) (val & 0xff);
            val >>= 8;
            outbuf[pos] = (byte) (val & 0xff);
            len -= 3;
            pos += 3;
        }
        return pos - pos0;
    }

    /**
     * Read the next valid byte from the input stream.
     * Buffer lots of data from underlying stream in input_buffer,
     * for efficiency.
     * 
     * @return the next byte, -1 on EOF, or -2 if next byte is '='
     *         (padding at end of encoded data)
     */
    private int getByte() throws IOException {
        int c;
        do {
            if (input_pos >= input_len) {
                try {
                    input_len = in.read(input_buffer);
                } catch (EOFException ex) {
                    return -1;
                }
                if (input_len <= 0)
                    return -1;
                input_pos = 0;
            }
            // get the next byte in the buffer
            c = input_buffer[input_pos++] & 0xff;
            // is it a padding byte?
            if (c == '=')
                return -2;
            // no, convert it
            c = pem_convert_array[c];
            // loop until we get a legitimate byte
        } while (c == -1);
        return c;
    }

    /**
     * Return the most recent characters, for use in an error message.
     */
    private String recentChars() {
        // reach into the input buffer and extract up to 10
        // recent characters, to help in debugging.
        String errstr = "";
        int nc = input_pos > 10 ? 10 : input_pos;
        if (nc > 0) {
            errstr += ", the " + nc + " most recent characters were: \"";
            for (int k = input_pos - nc; k < input_pos; k++) {
                char c = (char) (input_buffer[k] & 0xff);
                switch (c) {
                    case '\r':
                        errstr += "\\r";
                        break;
                    case '\n':
                        errstr += "\\n";
                        break;
                    case '\t':
                        errstr += "\\t";
                        break;
                    default:
                        if (c >= ' ' && c < 0177)
                            errstr += c;
                        else
                            errstr += ("\\" + (int) c);
                }
            }
            errstr += "\"";
        }
        return errstr;
    }

    /**
     * Base64 decode a byte array. No line breaks are allowed.
     * This method is suitable for short strings, such as those
     * in the IMAP AUTHENTICATE protocol, but not to decode the
     * entire content of a MIME part.
     * NOTE: inbuf may only contain valid base64 characters.
     * Whitespace is not ignored.
     */
    public static byte[] decode(byte[] inbuf) {
        int size = (inbuf.length / 4) * 3;
        if (size == 0)
            return inbuf;

        if (inbuf[inbuf.length - 1] == '=') {
            size--;
            if (inbuf[inbuf.length - 2] == '=')
                size--;
        }
        byte[] outbuf = new byte[size];

        int inpos = 0, outpos = 0;
        size = inbuf.length;
        while (size > 0) {
            int val;
            int osize = 3;
            val = pem_convert_array[inbuf[inpos++] & 0xff];
            val <<= 6;
            val |= pem_convert_array[inbuf[inpos++] & 0xff];
            val <<= 6;
            if (inbuf[inpos] != '=') // End of this BASE64 encoding
                val |= pem_convert_array[inbuf[inpos++] & 0xff];
            else
                osize--;
            val <<= 6;
            if (inbuf[inpos] != '=') // End of this BASE64 encoding
                val |= pem_convert_array[inbuf[inpos++] & 0xff];
            else
                osize--;
            if (osize > 2)
                outbuf[outpos + 2] = (byte) (val & 0xff);
            val >>= 8;
            if (osize > 1)
                outbuf[outpos + 1] = (byte) (val & 0xff);
            val >>= 8;
            outbuf[outpos] = (byte) (val & 0xff);
            outpos += osize;
            size -= 4;
        }
        return outbuf;
    }

    /***
     * begin TEST program ***
     * public static void main(String argv[]) throws Exception {
     * FileInputStream infile = new FileInputStream(argv[0]);
     * BASE64DecoderStream decoder = new BASE64DecoderStream(infile);
     * int c;
     * while ((c = decoder.read()) != -1)
     * System.out.print((char)c);
     * System.out.flush();
     * }
     *** end TEST program
     ***/
}
